1. Field of the Invention
The disclosed technology relates generally to photovoltaic cells, and more particularly to photovoltaic cells with plated metal contacts.
2. Description of the Related Technology
New concepts and fabrication processes are being developed for various aspects of silicon photovoltaic devices, aimed at higher efficiency devices that can also be manufactured at similar or lower cost compared to existing devices. One such area of development is in the metallization technology of photovoltaic cells. For example, plating processes have been proposed for forming metal contacts for photovoltaic devices, as an alternative to screen printing processes used in many devices.
Some plating processes, e.g., those used in forming front side metallization of silicon photovoltaic cells, include providing a dielectric layer, e.g., an antireflection coating over a front surface, and subsequently locally removing the antireflection coating, thereby exposing the underlying silicon surface at locations where metal contacts are to be formed in subsequent processes. In subsequent processes, for example, a metal plating process can be employed to form front side metal contacts in the exposed silicon regions. The antireflection coating can be locally removed, for example, via a laser ablation process.
In some technologies, the silicon front surface is textured to improve photovoltaic conversion efficiency. While advantageous for improving the conversion efficiency, the textured surfaces can introduce some process challenges. For example, a material, e.g., an antireflection coating, formed on a textured silicon surface can have nonuniformities that can pose difficulties in completely removing the material in subsequent processes due to, for example, shadowing effects and/or anisotropic nature of the subsequent removal process. As a result, it can be a challenge to completely remove the antireflection coating locally, without damaging the underlying emitter region. Incomplete removal of the antireflection coating can in turn pose additional problems, such as poor electrical contact of the metallization, poor adhesion and/or a high contact resistance. On the other hand, aggressive removal processes, which can damage the underlying emitter region can also have negative consequences, such as shunts and/or increased minority carrier recombination losses, which can lead to an overall degradation of cell performance. Thus, there is a need for photovoltaic devices and methods of fabricating the same, where the silicon front surface is textured for improved photovoltaic conversion efficiency, while having metal contacts that are formed on the front surface using a plating process without suffering from degraded electrical contact and or cell performance.
In photovoltaic cells with a selective emitter structure, i.e. an emitter structure with heavily doped regions underneath the metal contacts and lightly doped regions in between the metal contacts, an additional challenge is the alignment of the laser ablation pattern (for local removal of the antireflection coating) with the heavily doped regions of the underlying selective emitter structure.